1. Field of the Invention
The invention relates to an electrostatographic image forming apparatus employed in a copier, a facsimile, a laser printer and the like, and to a photosensitive member cartridge and a developer cartridge for use in the image forming apparatus.
2. Description of the Related Art
In some conventional image forming apparatuses for recording character or image data by supplying a developer to an electrostatic latent image formed on a photosensitive member (photosensitive drum) and transferring the visible image formed by the developer onto a recording medium, a cartridge-type process unit as disclosed in, for example, Japanese Patent Application Laid-open Nos. HEI 8-54786 and HEI 9-319285, (which correspond to U.S. Pat. Nos. 5,845,176 and 5,805,959, respectively) is employed in order to facilitate operations for maintenance, replacement, and the like.
According to the technology described in the aforementioned Japanese Patent Application Laid-open No. HEI 8-54786, after a photosensitive member cartridge incorporating at least a photosensitive member is set in a body (housing) of the image forming apparatus, a developer cartridge incorporating a developer containing chamber and a developing roller can be attached to and detached from the photosensitive member cartridge. The developer cartridge has a pair of forward and rearward guide pins that protrude from each one of the right and left sides of the developer cartridge.
The body housing has a first guide groove and a second guide groove that are formed in each one of the right and left side inner faces of the housing. The first and second guide grooves are elongated in up-down directions so that the forward and rearward guide pins of the developer cartridge can fit into the corresponding grooves from above. The shapes of the two guide grooves on each side inner face of the housing are arranged so that the developing roller of the developer cartridge comes into and out of the contact with the photosensitive drum of the photosensitive member cartridge while maintaining a predetermined posture. Therefore, the technology prevents the developer cartridge from impacting and damaging the photosensitive drum during replacement of the developer cartridge.
The technology described in the aforementioned Japanese Patent Application Laid-open No. HEI 9-319285 is intended to constantly form good quality images without fog and achieve a compact design of the process unit. The process unit set in the housing of the image forming apparatus incorporates a photosensitive member cartridge and a developer cartridge that are rotatably journaled by pins at positions which are across a straight line from the photosensitive drum, the straight line extending through the axis of the developing roller and substantially parallel to a tangent extending through a contact portion between the photosensitive drum and the developing roller, and which are above a straight line extending through the axis of the developing roller and the axis of the photosensitive drum.
In the latter technology, however, the provision of the journal makes it impossible to remove the developer cartridge alone. Moreover, the developer cartridge and the photosensitive member cartridge are connected by a tension spring urging them toward each other so that during image forming operation, the surface of the developing roller will be pressed against the surface of the photosensitive member (photosensitive drum) in order to form a visible image on the photosensitive member (photosensitive drum) in a developing area by supplying a thin layer of developer formed on the surface of the developing roller to an electrostatic latent image on the photosensitive member (photosensitive drum). Such a coupling arrangement between the developer cartridge and the photosensitive member cartridge also makes it impossible to replace the developer cartridge alone, for example, even if the developer (toner) runs out. That is, in such an occasion, the entire process unit must be replaced, which may be considered wasteful.
The former technology requires a user to hold the developer cartridge in a predetermined posture when inserting the forward and rearward guide pins, protruding laterally from the right and left sides of the case of the developer cartridge, into the vertically elongated first and second guide grooves formed in the right and left side inner faces of the apparatus body housing, or pulling the guide pins out of the grooves. If the developer cartridge in not held in the correct posture during the inserting or removing operation, the guide pins impinge on wall surfaces of the first and/or second guide grooves, so that the developer cartridge cannot be smoothly or easily inserted into, or pulled out of, the body housing.
Moreover, the guide pins, protruding from the side surfaces of the case of the developer cartridge, are subject to a problem of low mechanical strength. Further, the technology requires that the handling of the developer cartridge be facilitated by simplifying the operation of setting the developer cartridge into the press contact with the photosensitive member cartridge, and the operation of removing the developer cartridge therefrom, as much as possible.